The present invention relates to intraocular lenses and particularly to one-piece intraocular lenses.
For many years, the predominant method of treating a cataractous lens is to remove the diseased lens and replace it with an intraocular lens ("IOL"). Two surgical procedures are preferred for removing the diseased lens: extracapsular cataract extraction and phacoemulsification. Extracapsular cataract extraction involves removing the lens in a relatively intact condition by use of a vectus or similar surgical instrument. Phacoemulsification involves contacting the lens with the vibrating cutting tip of an ultrasonically driven surgical handpiece to emulsify the lens, thereby allowing the emulsified lens to be aspirated from the eye. Both surgical procedures require that the anterior lens capsule be cut to allow access to the lens itself and to allow the implantation of the replacement lens, and because the capsule bag is used to hold or retain the IOL in place after surgery, the opening should be as small as possible. Although extracapsular cataract extraction has been the preferred surgical technique, phacoemulsification is becoming increasingly popular, in part because of the relatively small (3-3.5 millimeter) tunnel incision that can be used with phacoemulsification.
A typical IOL comprises an artificial lens ("optic") and at least one support member ("haptic") for positioning the IOL within the capsular bag. The optic may be formed from any of a number of different materials, including polymethylmethacrylate (PMMA), polycarbonate and acrylics, and it may be hard, relatively flexible or even fully deformable so that the IOL can be rolled or folded prior to insertion. The haptics generally are made from some resilient material, such as polypropylene or PMMA. IOL's may be characterized as either "one-piece" or "multi-piece." With one-piece IOL's, the haptic and the optic are formed integrally as a blank and the IOL is then milled or lathed to the desired shape and configuration. The multi-piece IOL's are formed either by attaching the haptic to a pre-formed optic or by molding the optic around the proximal end of the haptic.
IOL's generally are designed with three criteria in mind; optical clarity, centration within the capsular bag and ease of surgical implantation. While current plastics such as PMMA have excellent clarity, the goals of ease of implantation at all surgical skill levels) and centration have been difficult to obtain consistently. Although ease of insertion is less of a concern when the surgical technique used is extracapsular extraction (with its relatively large incision), ease of insertion is extremely important with the small tunnel incision increasingly used with phacoemulsification. The designs of current IOL's generally trade off some insertion ease for improved centration without deformation and visa versa. For example, one predominant style of IOL includes a "J" or buttonhook-shaped haptic that is relatively easy to implant. However, the curled base of the J-shaped haptic contacts the capsular bag along only a very short radius, and tends to stretch and distort the capsular bag, resulting in zonular dialysis and possible optic displacement. The other predominant style of IOL includes a more gently curved, C-shaped haptic that contacts the capsular bag over a longer radius and tends not to induce capsular bag distortion to the same extent as J-shaped haptics. However, C-shaped haptics generally project outwardly from the diameter of the optic and, therefore, must fold backward over the optic during insertion. The relatively long length of C-shaped haptics requires that they be made relatively stiff to ensure centration, and this stiffness causes the haptic to resist bending or folding that when combined with the projection of the haptic over the optic, can cause the haptic to grab the wound tissue, making IOL's with C-shaped haptics relatively difficult to implant in the capsular bag when compared to J-shaped haptics, especially through the increasingly preferred small tunnel incision and small capsulorhexis used in phacoemulsification.
Many IOL designs have been developed in an effort to obtain an IOL that has excellent centration and is easy to implant. For example, U.S. Pat. Nos. 4,585,455, 4,608,049, 4,664,665, 4,664,667, 4,725,277, 4,731,079, 4,816,031 and 4,822,358 disclose an IOL having a thickened haptic attachment point and an enlarged or bulbous distal haptic tip. However, none of these patents discloses an IOL having a relatively flexible haptic or a haptic having a medial hinge or joint, and they all rely on the roundness of the bulbous tip to reduce tissue grabbing during insertion.
U.S. Pat. Nos. 4,446,581 and 4,676,794 disclose an IOL having a coil spring in the medial segment of the haptic to allow the haptic to flex. However, the distal segments of the haptic disclosed in these patents bow toward the optic. Therefore, there is minimal contact between the haptic and the capsular bag and capsular bag distortion can result.
U.S. Pat. Nos. 4,701,181, 4,710,195, 4,725,277, 4,932,967 and Re. 33,039 disclose IOL's having haptics with a medial segment of reduced cross-section area. However, the haptics disclosed in these patents all extend beyond the optic profile, requiring the incision to be enlarged to accommodate the haptics or risk potential haptic damage or excessive tissue (wound) contact.
U.S. Pat. Nos. 4,418,431, 4,504,981, 4,568,347, 4,575,374, 4,581,033, 4,591,358, 4,655,775, 4,828,558, 4,863,465 and 4,871,363 disclose IOL's having haptics with an elbow or "knee" joint to allow the haptic to flex more easily. However, none of these patents discloses the use of an elbow or knee joint of reduced cross-sectional area. These haptic are all relatively stiff, and rely on the geometry of the elbow or knee to facilitate flexing of the haptic.
U.S. Pat. No. 4,990,159 discloses an IOL with haptics having alternating cross-sectional area. While the design of the haptics in this patent may allow for more flexing of the haptic, this flexure is uniform across the entire length of the haptic and does not necessarily ensure that the haptics contact the capsular bag along a large radius. Furthermore, the haptic disclosed in this patent extends beyond the optic profile.
Another multi-piece IOL distributed briefly during the late 1970s by Medicornea Intraocular had a pair of squarely bent, modified C-shaped or L-shaped haptics. While the haptics on this lens appear to contact the capsular bag along a longer length of the haptic than the typical C-shaped haptic, the sharp corners and shape of the haptic made insertion difficult. In addition, the haptics have the same cross-section throughout their entire lengths, reducing flexibility. The disadvantages of this design are not surprising considering the fact that in the late 1970s, phacoemulsification was in its infancy and the predominant surgical technique for cataract removal was extracapsular extraction with sulcus placement of the IOL and centration rather than ease of insertion was the primary concern of the IOL designer.
Accordingly, a need continues to exist for an IOL having a haptic that tensions the capsular bag evenly and without deformation and that can be inserted more easily through the small tunnel incision used in phacoemulsification.